1. Field of the Invention
The invention relates to RFID communication systems which are selective for an individual transponder located in a predetermined target area, to the exclusion of other transponders, and to printers and other larger systems having such RFID communication systems.
2. Description of Related Art
Inductively coupled radio frequency identification (RFID) technology allows data acquisition and or transmission from and or to active (battery powered) or passive RFID transponders using RF magnetic induction. To read or write from and or to an RFID transponder, the RFID transponder is exposed to an RF magnetic field that couples with and energizes the RFID transponder through magnetic induction and transfers commands and data using a predefined “air interface” RF signaling protocol.
When multiple RFID transponders are within the range of the same RF magnetic field they will each be energized and attempt to communicate with the transceiver, potentially causing errors in reading and or writing to a specific RFID transponder. Anti-collision management technologies exist to allow near simultaneous reading and writing to numerous RFIDs in a common RF magnetic field. However, anti-collision management increases system complexity and cost. Further, anti-collision management is blind. It cannot recognize where a responding transponder is located in the RF magnetic field.
One way to prevent errors during reading and writing to RFID transponders without using anti-collision management is to isolate each RFID transponder from nearby RFID transponders. Previously, isolation of RFID transponders has used RF shielded housings and or anechoic chambers through which the RFID transponders are individually passed for isolated exposure to the interrogating RF magnetic field. This requires that the individual transponders have cumbersome shielding or a significant physical separation.
When RFID transponders are supplied attached to a carrier substrate, for example in RFID-mounted labels, tickets, tags or other media supplied in bulk rolls, Z-folded stacks or other format, an extra portion of the carrier substrate is required to allow one RFID transponder on the carrier substrate to exit the isolated field area before the next RFID transponder in line enters it. The extra carrier substrate increases materials costs and the required volume of the RFID media bulk supply for a given number of RFID transponders. Having increased spacing between RFID transponders may also slow overall throughput.
When the size or form factor of the utilized RFID transponder is changed, the RF shielding and or anechoic chamber configuration may also require reconfiguration, adding cost and complexity and reducing overall productivity.
There exists applications wherein it is desired to print on transponder-mounting media in the same target space in which the transponder is being read from or written to. This may be very difficult to accomplish if the transponder must be interrogated in a shielded housing or chamber.
Printers have been developed which are capable of on-demand printing on labels, tickets, tags, cards or other media with which is associated an RFID transponder. These printers have an RFID transceiver for on-demand communicating with the RFID transponder on the individual media. For the reasons given, it is highly desirable in many applications to present the media on rolls or other format in which the transponders are closely spaced. However, close spacing of the transducers exacerbates the task of serially communicating with each individual transponder without concurrently communicating with transponders on neighboring media. This selective communication exclusively with individual transponders is further exacerbated in printers designed to print on the media in the same space as the transponder is positioned when being interrogated.
Competition in the market for such “integrated” printer-transceiver systems and selective RFID interrogation systems has focused attention on minimization of overall costs, including reduction of the costs of individual RFID transponders, bulk RFID label and or tag supply carrier substrates, printers and or interrogators.
Therefore, it is an object of the invention to provide a system and method which overcomes deficiencies in such prior art.